Best way for this is to make the delay routine in assembly language and then link that to C. It is not predictable to make it in C becasue the C compiler can optimize the code in different ways and end up making the delay different.

You can look at the delay generator on my 8052.com web page to see how to create a simple delay routine in assembly language that is easily linked to and called from C.

See the delay generator here:
Link to Karas Page

Michael Karas